The present invention relates to planarization of semiconductor wafers using a chemical mechanical planarization technique. More particularly, the present invention relates to an improved system and method for detachably coupling a wafer carrier to a conveyor during the chemical mechanical planarization process.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. Wafers are commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that must be smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) systems are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, are typically an automated or semi-automated process involving multiple processing steps. The processing steps generally include transporting, aligning, polishing, washing and drying the wafers. In general, the wafers are received by the CMP system, processed and returned to a predetermined location, in a clean, dry, and uniformly planarized condition by the CMP system.
The processing step of polishing to achieve a uniformly planarized wafer can be performed sequentially at a number of processing stations having different degrees of material removal capability. The CMP systems often use a wafer carrier to hold the wafer during polishing. The wafer carrier is typically transported in a conveyor to the processing station(s). At the processing station(s), the wafer carrier is removed from the conveyor and the wafer thereon is brought into contact with a polishing pad rotating in the plane of the wafer surface to be planarized. Following the polishing and planarization operation, the wafer carrier is lifted off of the polishing pad and transferred back to the conveyor. The wafer carrier is coupled and uncoupled with the conveyor multiple times, especially when polishing occurs at multiple processing stations.
Some prior art systems for coupling wafer carriers to conveyors include multiple manipulative actions of the wafer carrier and/or the conveyor. Multiple steps result in a longer period of time required to couple and uncouple the wafer carrier and therefore the possibility of reduction in throughput of the CMP system. Further, multiple manipulations typically require multiple actuators or similar devices which present more maintenance and potential failure points in the CMP system. In addition, some prior art systems use actuators to maintain the coupling of the wafer carrier and the conveyor. In a loss of power and/or pneumatic air supply situation, the wafer carrier could be inadvertently detached from the carrier. Some prior art coupling systems also implement pins or other similar features that require precise alignment and may be bent or broken due to thrust loading that occurs when the wafer carrier is inserted and removed from the conveyor.
Accordingly, there is a need for systems and methods of detachably coupling the wafer carrier to the conveyor that involve few manipulative steps, allow for positive locking, and are rugged and easily alignable.
A system and method for detachably securing a locking mechanism to a housing is provided. In one preferred embodiment, the locking mechanism is fixedly coupled to a conveyor and is capable of being detachably coupled with a housing, such as, a wafer carrier. Manipulation of the wafer carrier with respect to the locking mechanism involves aligning an engagement mechanism on the wafer carrier to be adjacent the locking mechanism. Operating the locking mechanism to couple and uncouple the locking mechanism and the wafer carrier involves rotating the locking mechanism between two positions. The relatively few manipulative acts involved in coupling and uncoupling the wafer carrier to the conveyor create a fast and efficient coupling process that is easily alignable. In addition, the presently preferred locking mechanism does not include structural features that are easily bent or broken during the coupling and uncoupling of the wafer carrier to the conveyor. Further, the presently preferred locking mechanism provides positive locking action since it returns to, or maintains, a locked state when no actuators are acting upon it.
One presently preferred locking mechanism comprises a cam ring, a retention ring and a plurality of locking elements. The cam ring is slidably coupled to the retention ring and is concentric therewith. The cam ring includes a plurality of cam slots having an angular inner surface that are operatively positioned adjacent to a plurality of apertures in the retention ring. The locking elements are movably disposed within the cam slots adjacent the angular inner surface and are retained therein by the apertures.
The locking elements are movable between a first position defined as an unlocked position and a second position defined as a locked position. When the locking mechanism is rotated to an unlocked state, the locking elements are in the first position and a portion of the locking elements only protrude from the retention ring in a first direction. When the locking mechanism is rotated in the opposite direction to a locked state, the locking elements are in the second position and also protrude from the retention ring in an opposite direction. The housing includes an engagement mechanism that is adapted to engage the locking elements. When the locking elements are in the locked position, and the housing is positioned concentric with the retention ring and adjacent to the apertures therein, the locking elements engage the engagement mechanism.
Other features and advantages of the invention will be apparent from the drawings and the more detailed description of the invention that follows. The foregoing discussion of the presently preferred embodiments has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention.